A non-excitation operative brake is installed in a servomotor or the like as a safety device for when the motor is not in operation. A non-excitation operative brake is provided with a friction plate, an attraction plate, and an electromagnet, which are located on an outer peripheral portion of a rotating shaft to be braked and which are aligned along an axial direction of the rotating shaft, as is disclosed in, e.g., Patent Document 1.
The attraction plate, which is capable of moving along the rotating shaft, is pushed by spring force against the friction plate, which is attached to the rotating shaft, whereby brake force is exerted on the rotating shaft. The attraction plate is made of a magnetic material, and when the electromagnet facing the attraction plate is excited, the attraction plate is moved by magnetic attraction force in a direction away from the friction plate against the spring force, and the brake force is released.
In a non-excitation operative brake 100, typically, a fixed plate 102 is disposed in a determined position along the direction of an axis 101a of a rotating shaft 101 in order to reliably generate brake force, as shown in FIG. 4. An attraction plate 104, which is capable of moving in the direction of the axis 101a, is urged toward the fixed plate 102 by spring force of a pressing spring 105 in a manner in which a friction plate 103 is sandwiched between the attraction plate and the fixed plate, the friction plate being attached so as to be capable of moving in the direction of the axis 101a relative to the rotating shaft 101. When an electromagnet 106 is excited, the attraction plate 104 is attracted, the friction plate 103 becomes free to rotate, and the brake force on the rotating shaft 101 is released.